The present invention relates to process control apparatus. More particularly, it relates to improved digital output circuitry for use with a computer based process control system.
In the art of industrial process control, there have been provided systems wherein various parameters of a process are measured, compared with a desired value, and a difference therebetween used to derive a control or output signal. In a number of cases both the input, or measured variable, signals and the output signals are in the form of analog signals. In some cases, however, it is desirable to have the output signals in a digital form. The digital output signals may, in turn, be in four different formats. The signals may be in the form of latched holding relay closures; they may be in the form of momentary relay closures; or they may be in the form of solid state output signals either holding or momentary.